The present disclosure relates to an image forming apparatus utilizing electrophotography, such as a copier, a printer, a facsimile machine, or a multifunction peripheral having their functions integrated together. More particularly, the present disclosure relates to an image carrying member unit in which an image carrying member and a charging device having a charging roller are integrated into a unit, and to an image forming apparatus provided with such an image carrying member unit.
In conventional image forming apparatuses utilizing electrophotography, a charging device is incorporated for electrostatically charging the surface of a photosensitive drum which is an image carrying member. There are known charging devices of a corona charging type in which a photosensitive drum and a corona wire are arranged with no contact with each other to electrostatically charge the surface of the photosensitive drum by corona discharge, and charging devices of a contact charging type in which a charging member such as a charging roller is arranged in contact with or close to the surface of a photosensitive drum to electrostatically charge it. However, in recent years, to reduce the amount of discharged ozone, which is harmful to the human body, the contact charging-type charging devices, which discharge less ozone, have been increasingly used.
When a charging roller is brought into contact with the surface of a photosensitive drum in such a contact charging-type charging device, a configuration is typically adopted where the rotary shaft of the charging roller is supported on a bearing member which can reciprocate in a direction perpendicular to the surface of the photosensitive drum, and the bearing member is pressed by a biasing member such as a spring so that the charging roller is put in close contact with the photosensitive drum. With the above-described configuration, by applying a proper pressing force to the charging roller, it is possible to permit the charging roller to smoothly rotate by following the photosensitive drum as it rotates.